Political parties are not nearly as strong as many Americans, even some who are paid to observe the political process, realize. They cannot control the actions of every person who is elected to office under their banner. Hell, even party leadership in Congress can't really control their own caucus these days (certainly not like they used to). So as a preface to the following, realize that there is no centralized authority that can make this happen. It's a mindset that needs to be adopted, not a policy change that can be made.
There is little doubt that Democratic candidates are benefiting from the work of highly enthusiastic activists and supporters in the era of Trump. This is not entirely surprising; logically, if you can't get people fired up with the current status quo then you might as well throw in the towel and disband as a political party.
Unfortunately the Democratic Party has a long track record since 1980 of failing to deliver much of what its activist base wants. We get a lot of reaching across the aisle, bipartisan overtures, Triangulation, and incrementalism, but not much in the way of strong, forceful leadership on policy. And it's one of the major reasons it was so hard for Hillary Clinton, for example, to fire up turnout. Too many potential voters have picked up on the pattern of big promises and very minimal results. Obama half-delivered (the ACA is both a great political success and a half-assed attempt to cover everyone while still appeasing insurance companies) and it probably clinched his second term. Rightly (to her critics) or wrongly (to her supporters), Hillary Clinton was seen by too many people as the kind of New Democrat centrist who would get elected and not really push hard for anything progressive. Let's not argue whether or not that's true – at this point it doesn't matter. It's about the perception.
Some of it is unfair. The Democratic Party can indeed point to things it has done while in power. Some of it is fair, though. What do you expect LGBT people to think about your likelihood of fighting for them when it takes you 20 years in public life to come out and support gay marriage (once it is sufficiently popular)? What are black and hispanic voters going to think when the party speaks forcefully to them during elections and then…kinda tends to ignore things that they want thereafter? Misinformation doesn't help, but the perception is based at least somewhat on past experience. That is the first thing Democrats need to do a better job of: Stop making excuses (Russian bots! Fox News! Bernie Bros! Jill Stein!) even if those things really did hurt them in the past. Look at your own actions and ask sincerely, "How did WE fuck up? What can WE do better?"
This is a long way of saying that the wave of activism that pushed through recent Democratic successes is not likely to last long if the people elected revert to the old Let's Be Centrist ways. That's not someone coming from the outside and screwing the Democrats. That is a self-inflicted wound, pure and simple.
In Virginia, the newly-minted Democratic Governor gave a truly insane interview to the WaPo in which he claims that what voters really want is bipartisanship (at a time when the opposing party is not only totally uninterested in cooperating productively but is becoming a quasi-white nationalist movement pushing salted-Earth economic policies) and that he is worried about costs so he may not get behind Medicaid expansion. Medicaid expansion is, for the record, overwhelmingly popular in the general public and virtually unopposed among liberals.
You can excuse people who worked their asses off to push a very underwhelming Northam campaign over the finish line reading this and thinking, why did I bother? The obvious answer is that he's better than the Republican. This is undoubtedly true. But if Democrats haven't figured out yet that "This guy's an empty vessel, but the Republican is worse!" is not enough to fire up the people it needs to come out and vote for them, then they're never going to figure it out.
I don't mean to belabor the point or be unfair to Northam (who always was a moderate, so this isn't a turn for him) but just imagine how delusional you have to be as a politician to have lived through the last two years and think that the right response is to try harder to play nice with the right.
Doug Jones, for his part, started by stating that the sexual harassment claims against Donald Trump don't merit any more discussion. I get the whole "It's Alabama, he can't go full liberal on them" argument, and I understand it. But Donald Trump is as popular as the flu right now. Taking shots at Trump counts as kicking someone while they're down. Talk about a simple play – say "Yes, we need some answers on that" and you've committed to nothing but at least created the impression that you're serious about it – and Jones fumbled it. What is he trying to do? Signal that he's not interested in doing anything to irritate a deeply unpopular, failing demagogue of a president?
Parties are coalitions. Democrats rely very, very heavily on women, African-American and Hispanic voters, the young, and combinations thereof. And if you can't occasionally deliver for your key constituents – Republicans are flawless at this – then they are going to lose interest in working to get you elected. They won't turn on you and vote Republican necessarily; but they won't work their asses off for you when they expect that after the election you won't even pretend like you're serious about the things they care about.
The modern GOP, for all its awfulness, just understands governing and politics so much better than the Democratic Party that it's kind of embarrassing. Get elected, ram through some things that reward the people who got you elected, and then ask them to do it again next time by promising to deliver more. Try it sometime and you might be surprised how well it works, folks. Instead we get soft centrists telling us that if they act enough like Republicans they may win back some of the White Working Class. Oh boy!
It's too early to hit the panic button on any of the recently elected Democrats, but I know for absolute certain that "bipartisanship" is not what any voter wants. Voters want to win. They want to win elections and win something tangible in terms of policy as a result. Especially given the state of the contemporary GOP, nobody is going to be pleased by playing nice except David Brooks and Chuck Todd.
I don't advocate turning Democratic Primaries into purity tests, nor in intra-party squabbling throughout general elections. Objective one is absolutely: Get these bastards out. But that objective will be more difficult to accomplish the longer the party's office holders demur on taking off the gloves and showing a willingness to fight back. How can you expect the voters to fight hard for candidates who don't show a willingness to do the same?